Hot isostatic pressing, or “HIP,” is a method of manufacturing articles, which is used to reduce the porosity of metals and to increase the density of ceramic materials. The HIP process subjects the article to both an elevated temperature and an isostatic gas pressure in a high-pressure containment vessel. For pressurization, an inert gas is supplied, to reduce the any chemical reactions that may occur between the gas and the article. The vessel is heated, causing the pressure inside the vessel to increase. The heated, high-pressure gas is applied to the material from all directions, i.e., in an “isostatic” manner.
While various efforts are made during the HIP process to exclude reactive gasses, such as oxygen, from the containment vessel, experience has shown that it is difficult to remove all reactive gas molecules from the vessel prior to the introduction of the inert gas. Accordingly, though small, some amount (trace amounts, e.g., less than 10% by volume, or less than 5% by volume) of reactive gas remains in the containment vessel during the HIP process, which often results in some degree of contamination of the article. For example, where some amount of oxygen remains in the containment vessel, and the article is metallic, metal oxides may form on the surface of the article during the HIP process. Such oxides detrimentally affect the material properties of such articles, for example by altering the thermal conductivity thereof, and such oxides further interfere with subsequent manufacturing steps, such as plating, coating, and diffusion bonding.
In order to reduce the presence of reactive gasses in the HIP containment vessel, various attempts have been made to employ the use of reactive gas “getter” materials, i.e., materials that physically or chemically trap and remove the reactive gas molecules from the gas phase within the containment vessel. For example, U.S. Pat. No. 4,552,710 to Rigby et al. discloses a HIP process for MnZn ferrite magnetic transducer head, which employs the use of surrounding MnZn scrap pieces and an optional overlay of a getter material within the containment vessel in order to prevent the MnZn ferrite material from undergoing chemical change during the HIP process. U.S. Pre-grant Publication 2016/0184895 to Raisson et al. discloses a HIP process for densifying a pre-alloyed powder, which uses a getter to capture N2 and CO that may be evolved from the sintering of the powder. U.S. Pat. No. 3,992,200 to Chandhok discloses a HIP process using powdered metal in a mold, surrounded by a secondary pressure media in solid, particle form, which may include a getter material. Further, U.S. Pat. No. 3,627,521 to Vordahl discloses a HIP process using an iron-containing powdered metal in a collapsible container, wherein the collapsible container also includes a solid-form getter material.
It is thus apparent that the prior art remains deficient of suitable HIP apparatus and methods for inhibiting detrimental surface reactions, on a manufactured article undergoing HIP processing, caused by reactive gasses in the HIP containment vessel, without the need for close contact with scrap or packing materials and the like that could damage the article during HIP processing. The present disclosure advances the prior art by addressing at least this need. Furthermore, other desirable features and characteristics of the disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.